A patient with a high concentration of B-type natriuretic peptide (BNP) but normal N-terminal proBNP concentration: A case report.

OBJECTIVES: A 61-year-old female presented with non-typical chest pain. High levels of plasma B-type natriuretic peptide (BNP; result 3188 ng/L, reference range<100 ng/L, method Abbott Architect) were found, although she did not exhibit dyspnoea or other clinical symptoms of heart failure. Echocardiography did not provide an explanation for the elevated BNP concentrations. In follow-up, the chest pain complaints disappeared but BNP remained elevated at the same levels. The serum N-terminal proBNP (NT-proBNP) concentration appeared to be normal. This led us to doubt the accuracy of the BNP values. DESIGN AND METHODS: Possible interference was investigated with BNP and NT-proBNP assays from different manufacturers, various (auto)antibody tests, sample dilutions, addition of mouse serum and polyethylene glycol (PEG) precipitation. RESULTS: BNP and NT-proBNP concentrations were normal when measured using all other (NT-pro)BNP immunoassays. Serial dilutions of sample and addition of mouse serum did not alter the results. Specific (auto)antibody tests were negative. However, PEG precipitation showed the presence of a high molecular weight immunoreactive protein. CONCLUSIONS: We report a false positive BNP result possibly caused by a macro-BNP. This macro-BNP was only immunoreactive in the Abbott Architect BNP immunoassay. Clinicians should be aware of analytical interference when BNP results are constantly elevated in the absence of (non)cardiac causes.